1. Field of the Invention
The present invention relates to a drive control apparatus, a drive control method and an optical pickup apparatus in which drive of a motor is controlled. More particularly, the invention relates to a drive control apparatus and a drive control method which control the drive of a motor for moving a lens within an optical pickup apparatus that records or reproduces information on or from an optical disc by employing a semiconductor laser, and to the optical pickup apparatus.
2. Description of the Related Art
An optical disc apparatus has heretofore been known as an apparatus which is capable of recording and reproducing information of large capacities. An optical pickup apparatus which records and reproduces the information in the optical disc apparatus includes a semiconductor laser as a light source.
The optical disc apparatus records and reproduces the information by projecting a laser beam emitted from the semiconductor laser, onto an optical disc. In a reproduction mode, the optical pickup apparatus condenses the laser beam of predetermined power onto the optical disc and detects pits recorded on the optical disc, thereby to read the information recorded on the optical disc. In a recording mode, the optical pickup apparatus causes the semiconductor laser to emit light at power being higher than in the reproduction mode and modulates the laser power in accordance with the information to-be-recorded, thereby to form pits on the optical disc.
In order to record or reproduce the information at a high quality, the spherical aberration of an optical spot which is projected onto the optical disc needs to be corrected. An objective lens of a high numerical aperture, for example, a numerical aperture of 0.85 is employed especially for the optical disc called “Blu-ray Disc (hereinbelow, abbreviated to “BD”). Therefore, the allowable value of the thickness error of the protective layer of the optical disc is as strict as several μm or so, and the optical pickup apparatus (hereinbelow, also referred to as “optical pickup”) is required to have the function of correcting the spherical aberration.
A collimator lens is an optical component for converting divergent light emitted from the laser element, into a collimated beam. In this regard, there is, for example, a method of correcting the spherical aberration of the objective lens by moving the collimator lens in the direction of the optic axis thereof, and for example, a stepping motor is employed for the movement of the collimator lens.
A technique for correcting the spherical aberration and a technique for driving the stepping motor as stated above have hitherto been proposed. By way of example, an optical pickup apparatus disclosed in Japanese Unexamined Patent Publication JP-A 2005-302118 moves the collimator lens by a piezoelectric actuator in which piezoelectric ceramics are stacked.
An optical disc apparatus disclosed in Japanese Unexamined Patent Publication JP-A 2007-257720 detects the step-out of the stepping motor for moving the optical pickup in the radial direction of the optical disc, and it lowers the rotational speed of the stepping motor in a case where the step-out has occurred. The “step-out” is the phenomenon that, in such a case where a pulse frequency specified to the stepping motor has heightened, the torque of the stepping motor becomes insufficient, so the stepping motor does not rotate in accordance with a pulse voltage specified. This optical disc apparatus decides the occurrence of the step-out when a stepper pointer which indicates the rotation magnitude of the stepping motor has exceeded its upper limit, or when an address indicated by the stepper pointer and an actual address are different. The actual address is obtained in such a way that a reproduction signal from the optical pickup is decoded by a decoder.
According to a lens drive device for an optical pickup as is disclosed in Japanese Unexamined Patent Publication JP-A 2004-199780, the speed of the stepping motor is properly set in accordance with the ambient temperature of the stepping motor, in order to prevent the step-out ascribable to the fact that the viscous resistance of oil becomes high under a low-temperature environment. By way of example, the rotational speed of the stepping motor is lowered at a low temperature.
A drive apparatus for the optical pickup as is disclosed in Japanese Unexamined Patent Publication JP-A 2006-155839 corrects the spherical aberration of the optical pickup apparatus by moving the collimator lens. A support member which supports the collimator lens and which is urged by a coiled spring, has its movement distance from a reference position controlled by a nut member which is moved by the stepping motor. In a range up to the reference position after the abutment of the support member against a stopper portion, the nut member and the support member are in a non-contact state. When the nut member has abutted against the stopper portion, the stepping motor steps out, and the nut member stops at the reference position, so that the reference position can be determined. On this occasion, the support member for supporting the collimator lens is out of contact with the nut member. It is therefore possible to avoid a shock and a vibration on any optical component attributed to the step-out, and to lighten a load on the stepping motor.
It is desired in correction of spherical aberration of the objective lens to move the collimator lens at a high precision, to move the collimator lens at a high speed or to realize the correction at low price and at low power consumption.
Regarding these points, the optical pickup apparatus disclosed in JP-A 2005-302118 moves the collimator lens by employing the piezoelectric actuator. The piezoelectric actuator is easily applicable in case of a small movement magnitude. In case of a large movement magnitude, however, the piezoelectric actuator needs to be controlled by disposing a position sensor for obtaining positional information over the whole movement range. Further, since the piezoelectric actuator is expensive as compared with the stepping motor, the optical pickup apparatus has the problem that it is difficult of realization with small size and at low price.
The optical disc apparatus disclosed in JP-A 2007-257720 detects the step-out of the stepping motor. However, the address information of the optical disc needs to be obtained by decoding a reproduction signal with a decoder, and this gives rise to the problem that the optical disc apparatus cannot be made small in size. The stepping motor of this optical disc apparatus is used for moving the optical pickup itself, and it does not move the collimator lens in order to correct the spherical aberration. Further, the rotational speed can be lowered at the detection of the step-out, but there is the problem that the step-out cannot be prevented.
The lens drive device for the optical pickup as is disclosed in JP-A 2004-199780 can prevent the step-out ascribable to the fact that the viscous resistance of the oil becomes high under the low-temperature environment. However, in the same manner as in the optical disc apparatus disclosed in JP-A 2007-257720, the stepping motor of the lens drive device is used for moving the optical pickup itself, and it is not directed to moving the collimator lens for the purpose of correction of spherical aberration. Accordingly, there is the problem that the step-out of the collimator lens cannot be prevented.
The drive apparatus for the optical pickup as is disclosed in JP-A 2006-155839 grasps the reference position based on the step-out of the stepping motor, and it has the problem that the step-out cannot be avoided.